Colophon
About
Helping teams design software systems that survive real-world complexity.
This is a publication about software architecture, told through diagrams. Most writing on the subject leans on prose alone; the systems it describes are inherently spatial — flows, boundaries, and the trade-offs between them that a good diagram makes obvious and a paragraph only gestures at. The aim here is to put the diagram first and let the words do the work prose is actually good at: explaining why a structure is the way it is.
Each piece pairs an interactive diagram with the reasoning behind it — the constraints in play, the alternatives considered, and the failure modes that shaped the final design. The diagrams are not screenshots; they zoom, pan, and download, so you can take them into your own review. The intent is a reference you return to, not a feed you scroll past.
What this is about
- Risk-first architecture
- Decisions framed around what can fail and how much it would cost — not around what is fashionable.
- The diagram is the interface
- A system’s structure is spatial. The diagram is the contract teams reason about, not decoration bolted on after the prose.
- Evolutionary design
- Architectures that can change cheaply outlast ones that were “right” exactly once. Optimize for the next decision, not the last one.
- Surviving complexity
- Designing for the day the system is larger than any one person can hold in their head — where understandability is the scarce resource.
Who it’s for
Staff and principal engineers, architects, and engineering leaders who own consequential structural decisions — the people in the room when a choice is hard to reverse. If you run or sit in architecture reviews, weigh build-versus-buy, or have to explain a system to the team that will inherit it, this is written for you.
About Justin
Justin Coulston is a software architect who designs and reviews systems under real-world constraints — the deadlines, legacy, and uncertainty that never show up in a reference architecture. This site collects the diagrams and the reasoning behind them, in the open.
He also runs architecture review office hours: a standing slot to bring a real design, put the diagram on the table, and pressure-test it against the failure modes that matter.